Supraspinatus actions and functional roles.

[phillo]

I am a first year student, and i have recently studied the musculature of the shoulder, including the rotator cuff group. In learning the actions and functional roles of the supraspinatus muscle, a few sources such as my textbooks have stated that the supraspinatus initiates shoulder abduction. My lecturer says it has been known for years that this isn't the case; its only role is to be a synergist in keeping the humeral head centred in the glenoid fossa during arm movements. Just curious as to everyone's opinions on the actions and functional roles of the supraspinatus muscle, and if they agree with my lecturer.

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I found some Research done by Sugahara, 1974
According to him It has a Synergistic function for Elevation with flexion of the shoulder and also for extention. It's primary function is Elevation WITH Abduction, (throughout it's complete range) it is not at all active on abduction alone.
Hope that helps a bit

[skj]

I'm also completing my first year and we learned that the supraspinatus was active in EMG studies in the first 15 degrees of abduction/scaption. Also you have to consider that the deltoid is also the major participant. Yes this muscle helps to hold the humeral head in the glenoid fossa, as do all of the rotator cuff muscles. Another hypothesis is that the supraspinatus is partly responsible for the decellerating of the shoulder, ie. when you are throwing a ball. Also, do you guys also learn to do the "full can" exercise vs. the "empty can" just curious, there's been research that impingement can occur with this muscle in the empty can position. GOod luck. Sandra

[rayg]

We've always been taught in biomechanics that supraspinatus is an initiator of shoulder abduction simply because the deltoid is in a mechanically disadvantaged position to initiate abduction. For people who have supraspinatus problems who have to rely on deltoid to abduct their arm, they can only really accomplish this by first laterally flexing their trunk to the side of the shoulder they want to abduct, which effectively 'passively' abducts the shoulder to a point where deltoid can act as an abductor. Any half-decent biomechanics or functional anatomy text should say pretty much the same thing... Cheers, Ray